I have never done any dyno testing of 3 hole spacers.We did do a few pulls with different 4 hole spacers and open spacers.remember when nascar use a spacer/restricter? The 4 hole spacer that has has porting done sometimes adds power.what I will try to describe is:
looking through the top of the spacer you see 4 holes with a flat bridge between the holes.Under side looking up you see the center cross has been ported to a point like a bullet shape. we tested same thing with all 4 holes chamfered and spacers with no dividers. The particular engine we were testing liked having the bullet nose cross the best.
some intakes are available with an inverted bullet on the intake floor.It does not work in every situation.